Developing effective reproductive health interventions for women in treatment for substance use disorders has tremendous potential to improve women and children's health. In the US nearly half (51%) of all pregnancies are unplanned (Finer and Zolna, 2014) and a recent study of pregnant women entering opioid medication-assisted treatment found much higher proportions - 86% described their current pregnancy as being unintended (Heil et al., 2011). Women with unintended pregnancies had higher rates of recent substance use and almost all (90%) had a history of prior treatment for substance use disorders. Thus, substance use treatment programs may be promising sites to address contraception and reproductive health. There is a paucity of interventions that specifically focus on preventing unintended pregnancies among women with substance use disorders. This study proposes to use the Health Belief Model (HBM; Rosenstock, 1974) to guide the development of a brief peer-led reproductive health intervention that will be integrated into the substance use treatment setting. Additionally, the intervention will specifically focus on uptake of long acting reversible contraceptive methods as they are considered to be the most effective method of reducing rates of unintended pregnancies (Trussel et al., 2009; Trussell, 2012). Through using mixed methods this study will address the following aims: 1) to use formative methods to better understand contraceptive behaviors and to develop a brief peer-led intervention to prevent unintended pregnancies among women of reproductive age entering opioid medication-assisted treatment; 2) to assess acceptability, feasibility and initial efficacy of the behavioral interventon; and 3) to conduct exploratory analyses to identify the HBM constructs that are most influential on LARC use. Intention-to-treat analyses will be used to assess change in LARC use between baseline and 3 and 6 month follow-up and will test the following hypotheses: participants in the intervention group will be more likely to follow-up with a family planning visit; and participants n the intervention group will be more likely to initiate LARC methods. The long-term goals of this Stage I project are: 1) an intervention that can be tested formally in a larger scale Stage II tria and 2) an enhanced understanding of the HBM constructs involved in contraception decision making and LARC uptake and use.